For an object shot via an image pickup optical system, light emitted from one point cannot be converged to another point and has a minute spread due to an influence of a diffraction, an aberration, or the like that occurs in the image pickup optical system. Such a minutely-spread distribution is referred to as a PSF (point spread function). Due to the influence of the image pickup optical system, the shot image is formed with the PSF convolved with the image, and accordingly, the image is blurred and its resolution is deteriorated.
Recently, the shot image is typically stored as electronic data, and image restoration has been proposed which corrects an image deterioration caused by the image pickup optical system by performing image processing. In order to correct the image deterioration caused by the image pickup optical system, it is necessary to obtain accurate OTF information of the image pickup optical system. In reality, however, an object shot by an image pickup apparatus is typically a three-dimensional object with a depth direction instead of a planar object. PTL 1 discloses an optical modulator provided in an image pickup optical system and a method of performing image processing while enlarging a depth of focus. PTL 2 discloses a method of acquiring a distance map of a shot image to perform image processing depending on a distance.